but hopefully, there is a good reason for her not returning your call.  OTOH, she may have discovered something about you that she doesn't like.  Not that you've done anything real bad, just her opinion.  I would wait a day or two after the last call, and if you haven't yet heard from her, it's probably time to move on.  There are plenty of others out there.

Swim

The answers already posted show how unclear your OP original post was.  You need to provide relevant details.  

Some providers have email, telephone, text, twitter, smoke signals and all the options but they won't bother setting up their VM.  Or they deliberately let their VM fill up and never check it.  Some deal exclusively by phone.  Everyone is different.  Even if telephone / VM is their only or preferred contact method, they might be on vacation ... even just 3 days with family or friends could mean being incommunicado with phone and computer turned OFF.    

They do not all sit by their phone waiting for our calls.  They have real lives and other things to do.

Send an email. Wait a month. Move on